Pulmonary arterial size and response to sildenafil in chronic thromboembolic pulmonary hypertension.

Background: Relative area change (RAC) of the proximal pulmonary artery is a measurement of pulmonary artery distensibility and has been shown to correlate with vasoreactivity studies in patients with idiopathic pulmonary arterial hypertension. We have previously noted a relationship between invasive hemodynamic vasoreactivity testing and long-term response to sildenafil in patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH). We therefore set out to determine whether RAC can provide useful correlatory non-invasive data.

Methods: Patients recruited to a randomized, controlled trial (RCT) of sildenafil at 40 mg 3 times daily underwent additional magnetic resonance imaging (MRI) at the baseline of the trial. Eighteen patients had an MRI that led to a diagnosis of inoperable distal CTEPH or significant residual CTEPH post-operatively. The primary end-point was improvement in 6-minute walk test (6MWT) with secondary end-points of right heart catheterization-based hemodynamics, N-terminal pro-brain natriuretic peptide (NT pro-BNP) and functional class. RAC assessed by MRI was correlated with trial end-points.

Results: Fourteen subjects with baseline MRI completed the protocol. RAC was the only baseline variable that correlated at 1 year to the primary end-point of improvement in 6MWT (r = 0.7, p = 0.006), and also to a change in NT pro-BNP (r = 0.59, p = 0.03). Using a cut-off of RAC over 20% there was an 87.5% sensitivity (95% confidence interval [CI]: 45% to 100%) and a 66.7% specificity (95% CI: 22% to 96%) for an improvement in 6MWT of >40 meters.

Conclusions: RAC correlates with functional response to sildenafil, as measured by the 6MWT, and improved heart function, as measured by NT pro-BNP. RAC shows potential in understanding and possibly predicting treatment response.